ChemInform Abstract: Reaction of Propa‐1,2‐dienylphosphonates with Ethylenediamine.

Abstract

Alkenylphosphonates containing aminoorganyl groups in the β-position with respect to the phosphoryl fragment are promising from the practical viewpoint as biologically active compounds. With a view to obtain new derivatives of this series, we examined reactions of allenylphosphonates with ethylenediamine. The reaction of diethyl propa-1,2-dienylphosphonate (Ia) with ethane-1,2-diamine was accompanied by strong heat evolution, and it led to the formation of a thick oily product. The IR spectrum of this product lacked absorption band at 1960 cm typical of the C=C=C triad, but bands corresponding to stretching vibrations of C=C bond (1635 cm) and NH and NH2 groups (3200–3360 cm) appeared. In the H NMR spectrum of the product (DMSO-d6) we observed a doublet signal at δ 1.95 ppm (3H, CH3C=, JPH = 1.9 Hz), which indicated the absence of terminal H2C= group. Also, a doublet signal was present at δ 3.41 ppm (JPH = 12.5 Hz) due to CH= proton in the α-position with respect to phosphorus, whereas there was no signal assignable to protons in PCH2 methylene group with a characteristic coupling constant JPH of 18– 22 Hz. These findings allowed us to exclude theoretically possible imine structure [1, 2]. Signals from the ethoxy groups in the phosphoryl fragment were located in the expected regions, at δ , ppm: 1.03 t (6H, CH3CH2, JHH = 7.1 Hz) and 4.01 m (4H, CH2O). Only one phosphorus signal was present at δP 27.5 ppm in the P NMR spectrum (DMSO-d6) The above data led us to conclude that phosphonate Ia reacts with ethane-1,2-amine via attack by the amino nitrogen atom in the latter on the central sp-hybridized carbon atom of the cumulene fragment to produce enamine structure, diethyl 2-(2-aminoethylamino)prop-1-en-1-ylphosphonate (II) (Scheme 1). It should be noted that compound II is capable of undergoing enamine–imine tautomerism, depending on the solvent. In CDCl3, the adduct exists as mixtures of several tautomers, as follows from the presence of additional signals in the P NMR spectrum, δP 22.44, 22.62, 26.07, 26.58, and 26.67 ppm. In the H NMR spectrum of a solution in CDCl3 we observed a doublet from methylene protons at δ 2.54 ppm (2H, PCH2C, JPH = 22.4 Hz), while no signal assignable to terminal methylene group H2C was present. These data indicated formation of imino tautomer III. The presence of numerous signals in the P NMR spectrum (CDCl3) may also be attributed to Z/E isomerism of different tautomers. The H NMR spectrum was also strongly complicated. On the other hand, we cannot rule out initial isomerization of allenylphosphonate Ia into propynylphosphonate, followed by addition of ethylenediamine to the triple bond. Enamine II was also synthesized by reaction of diethyl prop-2-yn-1-ylphosphonate with ethylenediamine. By reaction of ethylenediamine with 2.5 equiv of diethyl, diisopropyl, and dibutyl propa-1,2-dienylphosphonates Ia–Ic we obtained bis-phosphonates IV–VI (Scheme 2). The P NMR spectra of IV–VI contained only one signal. Compounds IV–VI displayed in the ISSN 1070-4280, Russian Journal of Organic Chemistry, 2013, Vol. 49, No. 9, pp. 1399–1400. © Pleiades Publishing, Ltd., 2013. Original Russian Text © N.G. Khusainova, E.P. Pogodina, A.V. Gerasimov, 2013, published in Zhurnal Organicheskoi Khimii, 2013, Vol. 49, No. 9, pp. 1415–1416.